Electrical System Confusion!

[5.3Avalanche]

I have a 2008 Silverado, 5.3FF, A4, 4x4, ext cab, standard box.

 

The other day I drove the truck in the morning and it had no issues. Went to start it up to leave again about 8 hours later and it fired up with no issues. Pulled about 50 feet out my laneway and it just died. Motor turned off like I turned the key off. No hiccups or anything like that. So I tried cranking it again immediately and it wouldn't start. Lots of juice in the battery, but it wouldn't fire. Let it sit for 5 min, came back and it started right up! Put it in drive, drove another 50 ft then shut off again like I turned the key off. So then the troubleshooting began. The first thing I noticed was that the fuel pump was not priming when I put the key to the on position like it always used to. No noise, no click, nothing. So I checked the relays, and everything was good. It appeared that power was leaving the main fuseblock and going to the pump. But I also noticed that my right rear tail lights were dimmer than the left rear tail lights. Odd. So I got back in and tried cranking the truck again. It fired, and the starter stayed on! It just kept cranking even though my hand was off the key. At this point I wasn't sure what to do. I called my buddy who's a mechanic and he diagnosed the fuel pump as being bad. So the next day I put in a new fuel pump myself. Put the key to the on position, and nothing again. Periodically if you wait a while and then put the key to the on position, the pump will click briefly, but won't prime. I get no pressure increase at the fuel rail at all.

So then I tried checking fuses and wiggling harnesses all over the truck to see if I had a short somewhere. No luck with that.

 

Tonight I plan on swapping out the battery and seeing if that's the case. I'm also going to check out the master fuse and see if there is any odd arcing. The last thing I have in my mind to check will be the grounds throughout the truck. I'm not sure I know where they all are but I'm going to trace each harness, loosen each ground, clean it off and reattach it.

 

Have any of you experienced anything like what I have? Any other additional ideas from what I've already tried?

 

Thanks in advance.

[gmtech4]

computer controlled truck,,,,,

 

scan the truck for codes ,,,you are going in the wrong direction,,,,,,get alldata.com

[8.1HD/ALLISON]

Codes?

 

Sent from my LGL86C using Tapatalk

[chupe442]

As much as I hate the "get codes" replies..... We are living in a computer driven age. Code reads are a must unless you find where the factory smoke left a trail... Sorry! Good luck!

[5.3Avalanche]

Turns out the issue was an intermittent and corroded ground on the G300 harness. This powers all of the items in my description above (right side tails, blinker, fuel pump, trailer harness etc). Removed, cleaned, reinstalled and everything was good to go. Looks like my assessment of things to try was correct. Truck was not throwing any codes by the way for all those with code suggestions.

Cheers.

[8.1HD/ALLISON]

Glad you found it. Grounds can cause serious headaches.

 

Sent from my LGL86C using Tapatalk

[indiana salt racer]

HELP!

 

Ok I give up where is G300 located? I found a single ground under the Driver A pillar on a body mount, nothing under the B pillar and 2 singular grounds on the LR body mount. Others keep talking about bunches of grounds in certain locations, but all I find are singles.

 

Mine wil run and start as long as I have my foot on the brake, take it off and it dies.when ABS light comes on.

Lastly my son saw and videoed an electric ARC formed at the 7 o'clock position of the power brake Booster. wierdest thing I have ever seen in my life.

So far new Alt, new fuel pump, changed FPCM (the reinstalled original one to get OE fuel pressure). We even disconnected the ABS pump, the ABS hyrdaullic sensor next to the ABS pump. Same thing still happens. Pulled all the ABS and brake fuses. still happens. Added ground strap from Alt bracket and firewall, still happens.

Only other thing we did was replaced the steering column used original theft sensor, tumbler, brake release shifter, and original shifter.

Order of repair was FP, FSCM, then Column.

 

2014 Suburban 1500 4x4 LT 5.3

[davester]

maybe spend the couple bucks for an online subscription to the full-service manual for your truck.  it has pictures of where all the grounds are located (well, I don't know about if it includes this for your truck, but it does for mine)...  It has connector pinouts, and plug locations, wiring diagrams and diagnostic procedures for a whole lot of different problems.

 

Diagnose before throwing parts at it...

[indiana salt racer]

Gee thanks, I have one and when it searches for G300 it comes up empty. It finds G100, 101, 200, 201, 203,204, 400, 401 and others.

Oh and GM never discusses random ground problems in their electrical sections of any of the dozens of factory service manuals I posses. I was impressed with the vast knowledge that forum members have with idiosyncrasies that develop on vehicles that are out of warranty and the genuine fixes they resolve.

 

also I never found any mentions of arc welding of power brake booster anywhere in the manual either.

 

That's why I asked you knowledgeable folks the simple question of where it was located.

If I knew I wouldn't have to ask.

Man, rough crowd.

[davester]

Well, if it's not in the FSM, I'm not sure how anyone will be able to tell you where G300 is, as the FSM is what names that specific groundf.  I do know the paper version can be difficult to find where things are, if you don't happen to know what term GM uses for it, or what they might happen to group it with, and the online version probably isn't a long better.

 

The FSM for my '04 Sierra has a section called "Wiring Systems", which has a diagram of zones (so, rough are where G300 would be), how to test for continuity, short to ground or voltage, how to probe connectors, and a how bunch more info on how to diagnose electrical problems.

 

And are you even sure there is G300 ground?  For my truck, I find a G302, G304, G305, G306, G310 and G390), and in the same Wiring Systems section, there is a subsection called "Power and Grounding Component Views", which has a bunch of pictures showing where the various power and ground connections are located in the truck.

 

Nobody is going to know about why you happen to have a short somewhere around your power booster.  You have to go through the wiring in the area and see where something might have rubbed through,  Blown fuses would help guide you to which wires might be causing the problem, by tracing through the wiring diagram for the fuse, and going from the wiring diagram to the harness that wire is in.

[indiana salt racer]

Not around the power booster it is the power booster arcing to itself.

Guess I'm diving under the dash...

[riverbanks]

The arcing there is a path,a short to ground,trailer brake controller?chaffed wire?worst case,is the path could be the brake lines

[muddkatt]

Let me ask if you are referring to the "2014 Suburban 1500 4x4 LT 5.3"? If so, your post is in the wrong forum section. You should ask in this section: https://www.gm-trucks.com/forums/forum/190-2015-2019-tahoesuburbanyukon-troubleshooting/

[indiana salt racer]

they didn't change the body style til the 15 Suburbans and Tahoe. So I'm not sure why you ant me to post it in the 15-19 group?

[indiana salt racer]

 

Added a ground cable from the Alt bracket to the firewall.

Added a ground from firewall to the highest Ohm reading bolt on the front of the fuse box.

 

At least it is running and driving and the lights work and signals too and no more arcs from the booster.

Was able to plug the EBCM back in and it didn't mind that.

G300 ground is a smaller wire that goes under the A pillar on the frame at the body mount. Cleaned it didn't make any difference before the new grounds.

 

Damn weird problems and so many people having them on these expensive vehicles is sad....

 

Looks like all the computer controls depend on grounds , was better in the 80s and 90s when relays turned stuff on when needed and not PC boards hunting for a dedicated wired ground to turn on a device. Or I'm just getting old. These things seem like the C3 vettes, they always had ground problems to make everything work properly.